Hello @Lildreas ,
This will depend on the formats and expected usage of these assets. Are these hand-placed Unreal assets (foliage, models, characters, etc.) or are they photogrammetry surveys / large-scale datasets?
From what it sounds like, our georeferenced sublevels framework may be of interest to you. This is a way to place different Unreal sublevels, each filled with typical Unreal assets, across the world. In playmode, as you approach any one of the specific sublevels, it dynamically loads in with all the expected Unreal assets. In your case, you may wish to have a different sublevel represent each of your airports.
On the other hand, if your building assets are large datasets that would particularly benefit from Cesium’s efficient LOD-based streaming, we encourage you to try both approaches you mentioned, i.e., using a single large tileset vs ~30 smaller ones. The advantage of a single large 3d tiles dataset will be potentially better streaming-performance and optimization. Additionally, it may be difficult to manually position 30 custom buildings in Cesium Ion (this is to georeference them properly before they are imported to Unreal). We currently do not have a great way to import 3D tiles datasets as non-georeferenced models that can be conveniently moved and placed within the Unreal editor.
I think your best bet is the first approach (georeferenced sublevels), but feel free to elaborate on your use-case and constraints if these options do not work well!